Multi-layer, attenuated phase-shifting mask

ABSTRACT

The present invention provides an attenuated phase shift mask (“APSM”) that, in each embodiment, includes completely transmissive regions sized and shaped to define desired semiconductor device features, slightly attenuated regions at the edges of the completely transmissive regions corresponding to isolated device features, highly attenuated regions at the edges of completely transmissive regions corresponding to closely spaced or nested device features, and completely opaque areas where it is desirable to block transmission of all radiation through the APSM. The present invention further provides methods for fabricating the APSMs according to the present invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/741,460,filed Apr. 27, 2007, now U.S. Pat. No. 7,611,809, which is scheduled toissue on Nov. 3, 2009, which is a continuation of application Ser. No.11/154,265, filed Jun. 15, 2005, now U.S. Pat. No. 7,226,708, issuedJun. 5, 2007, which is a continuation of application Ser. No.10/629,641, filed Jul. 29, 2003, now U.S. Pat. No. 6,908,715, issuedJun. 21, 2005, which is a continuation of application Ser. No.09/809,720, filed Mar. 15, 2001, now U.S. Pat. No. 6,599,666, issuedJul. 29, 2003. The disclosures of the previously referenced U.S. patentapplications referenced are hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to photolithography techniques used insemiconductor device manufacturing processes. Specifically, the presentinvention relates to a multi-layer, attenuated phase-shifting mask orreticle that reduces problems associated with side lobe printing inareas including closely spaced or nested features, while maximizingresolution and depth-of-focus performance for isolated features of asemiconductor device.

2. State of the Art

Photolithography processes are essential to the fabrication of state ofthe art semiconductor dice. Such processes are used to define varioussemiconductor die features included in semiconductor dice and generallyinclude exposing regions of a resist layer to patterned radiationcorresponding to the semiconductor die circuit feature to be defined ina substrate underlying the layer of resist. After exposure, the resistlayer is developed to selectively reveal areas of the substrate thatwill be etched to define the various device features while selectivelyprotecting those areas of the substrate which are not to be exposed tothe etching process. In order to properly form a radiation pattern overa resist layer, the radiation is generally passed through a reticle ormask which projects the semiconductor die feature pattern to be formedin the resist layer.

Various types of photolithographic masks are known in the art. Forexample, known masks often include a transparent plate covered withregions of a radiation blocking material, such as chromium, which definethe semiconductor die feature pattern projected by the mask. Such masksare called binary masks since radiation is completely blocked by theradiation blocking material and fully transmitted through thetransparent plate in areas not covered by the radiation blockingmaterial. However, binary masks cause significant fabrication problems,particularly where semiconductor die dimensions shrink below 1 μm.

As the pattern features of a binary mask are defined by boundariesbetween opaque, radiation blocking material and material which iscompletely radiation transmissive, radiation passing through a binarymask at the edge of a pattern feature will be diffracted beyond theintended image boundary and into the intended dark regions. Suchdiffracted radiation prevents formation of a precise image at thefeature edge, resulting in semiconductor die features which deviate inshape or size from the intended design. Because the intensity of thediffracted radiation drops off quickly over a fraction of a micron,diffraction effects are not particularly problematic where semiconductordice have dimensions on the order of 1 μm. However, as featuredimensions of state of the art semiconductor dice shrink well below 0.5μm, the diffraction effects of binary masks become terribly problematic.

Another type of mask known in the art is an attenuated phase shift mask(APSM). APSMs were developed to address the diffraction problemsproduced by binary masks and are distinguished from binary masks inthat, instead of completely blocking the passage of radiation, the lesstransmissive regions of the mask are actually partially transmissive.Importantly, the attenuated radiation passing through the partiallytransmissive regions of an APSM generally lacks the energy tosubstantially affect a resist layer exposed by the mask. Moreover, thepartially transmissive regions of APSMs are designed to shift thepassing radiation 180° relative to the radiation passing through thecompletely transmissive regions and, as a consequence, the radiationpassing through the partially transmissive regions destructivelyinterferes with radiation diffracting out from the edges of thecompletely transmissive regions. Thus, the phase shift greatly reducesthe detrimental effects of diffraction at the feature edges, therebyincreasing the resolution with which sub-micron features may bepatterned on a resist layer.

A conventional APSM 4 is illustrated in drawing FIG. 1. As can be seen,the APSM 4 includes a transparent substrate 6 coated with a partiallytransmissive material 7 (to ease description, drawing FIG. 1 provides agreatly simplified APSM). The partially transmissive material 7 has beenpatterned to form a completely transmissive region 8 and two attenuatedregions 10 a, 10 b. The attenuated regions 10 a, 10 b of a typical APSM4 are typically designed to allow the passage of between about 4% (lowtransmission) and 20% (high transmission) of the incident radiation 12.The partially transmissive material 7 forming the attenuated regions 10a, 10 b is formed to a thickness that shifts the incident radiation 12one hundred eighty degrees (180°) out of phase.

Also provided in drawing FIG. 1 is a graph 16 illustrating theelectromagnetic intensity (plotted on the vertical axis) of theradiation passing through the APSM 4 relative to the position (plottedon the horizontal axis) on the surface of the exposed resist. As shown,the intensity curve 18 includes a first component 20 located primarilybetween the edges 22 a, 22 b formed between the attenuated regions 10 a,10 b and the completely transmissive region 8 of the APSM 4. The firstcomponent 20 of the intensity curve 18 corresponds to theelectromagnetic intensity of the radiation passing through thecompletely transmissive region 8 of the APSM 4 illustrated in drawingFIG. 1. As can be seen in the graph 16, the electromagnetic intensity ofthe radiation falls to zero at points 24 a, 24 b, which are near theedges 22 a, 22 b. Points 24 a, 24 b correspond to the locations wherethe magnitudes of the in phase radiation passing through the completelytransmissive region 8 and the out of phase radiation passing through theattenuated regions 10 a, 10 b are equal. Beyond points 24 a, 24 b andmoving away from the edges 22 a, 22 b, the electromagnetic intensity ofthe transmitted radiation grows again to a steady value as indicated bythe second curve components 26 a, 26 b. The second curve components 26a, 26 b represent the electromagnetic intensity of the radiation passingthrough the attenuated regions 10 a, 10 b of the APSM 4.

The electromagnetic intensity represented by the second curve components26 a, 26 b is also known as “ringing effects,” and one significantdisadvantage of APSMs is that such ringing effects become much moresevere as feature density of an APSM increases. As device featuresdesigned into an APSM are spaced closer and closer together, the ringingeffects of adjacent device features begin to overlap, and as the ringingeffects overlap, the electromagnetic intensity of such ringing effectsbecomes additive. These increased ringing effects are known as “additiveside lobes,” “additive ringing effects,” or “proximity effects.” Incontrast to isolated ringing effects produced by isolated devicefeatures, the electromagnetic intensity of additive side lobes createdby closely spaced (i.e., ≦0.5 μm) or nested device features oftenbecomes sufficiently intense to cause printing of the resist layer,which is commonly termed “side lobe printing.”

Illustrated in drawing FIG. 2 is the additive ringing effects associatedwith conventional APSMs having closely spaced feature formations. Asillustrated in drawing FIG. 2, a second APSM 30 includes a transparentsubstrate 32 coated with a partially transmissive phase-shifting film 34(again, for ease of description, drawing FIG. 2 provides a greatlysimplified APSM). The partially transmissive phase-shifting film 34 hasbeen patterned to form four attenuating regions 36 a-36 d and threecompletely transmissive regions 38 a-38 c, which are closely spaced.Radiation 39 incident on the APSM 30 passes through the completelytransmissive regions 38 a-38 c and the attenuated regions 36 a-36 d andimpinges upon the surface of the resist layer to be patterned (notillustrated in drawing FIG. 2).

Included in drawing FIG. 2 is a graph 40 illustrating theelectromagnetic intensity of the radiation incident upon the surface ofthe resist layer to be patterned. The graph 40 includes an intensitycurve 42 made up of various components, with the first components 43a-43 c illustrating the electromagnetic intensity of the radiationpassing through the completely transmissive regions 38 a-38 c of theAPSM 30, the second components 44 a, 44 b illustrating theelectromagnetic intensity of the ringing effects produced by theradiation passing through the isolated attenuated regions 36 a, 36 d,and the third components 46 a, 46 b illustrating the electromagneticintensity of the additive side lobes produced by the dense featurearrangement formed by the closely spaced attenuated regions 36 b, 36 c.As can be seen in drawing FIG. 2, the magnitude of the second components44 a, 44 b (represented by line “I₁”), which illustrate the intensity ofthe ringing effects produced by isolated attenuated regions 36 a, 36 d,is significantly lower than that of the third components 46 a, 46 b(represented by line “I₂”), which illustrate the electromagneticintensity of the additive side lobes.

Provided in drawing FIG. 3 is a cross-sectional view of a partiallyfabricated structure 50 after exposure through the APSM 30 illustratedin drawing FIG. 2. The partially fabricated structure 50 includes asemiconductor substrate 52 and a developed resist layer 54. Thedeveloped resist layer 54 exhibits a set of depressions 56 a, 56 bresulting from the relatively high electromagnetic intensity of theadditive side lobes caused by the dense feature arrangement of the APSM30. As device feature density increases, so will the intensity of theadditive side lobes and the extent to which the resist layer ispatterned due to exposure to additive ringing effects. Thus, depressionsin the resist layer due to additive ringing effects may, in somesituations, degrade the resist layer to such an extent that entiresemiconductor dice become unusable due to damage incurred during asubsequent etch process.

As is well known in the art, the ringing intensity is inversely relatedto the attenuation of the partially transmissive material used in APSMs.Increasing the attenuation of the partially transmissive material will,therefore, decrease any resultant ringing effects, while decreasing theattenuation will increase any resultant ringing effects. Thus, theintensity of additive side lobes produced by closely formed features inan APSM may be decreased simply by increasing the attenuation of thepartially transmissive regions included therein.

However, increasing the attenuation of the partially transmissive areasof APSMs also has significant drawbacks. For example, increasing theattenuation of the partially transmissive areas decreases printperformance as well as the resolution and depth-of-focus achievable bythe APSM. Reduction of depth-of-focus and resolution characteristics ofan APSM are particularly problematic in the fabrication of state of theart semiconductor devices, which requires that an APSM accuratelyproject images corresponding to sub-0.5 μm device features whilefocusing such images through relatively thick layers of resist. Inaddition, even with the most precise fabrication equipment, sub-microndeviations from the optimum focus position of the APSM relative to theresist layer to be patterned will occur, and decreasing thedepth-of-focus of an APSM increases the probability that fabricationdefects may result from such slight deviations. Therefore, increasingthe attenuation of the partially transmissive materials included instate of the art APSMs requires a careful compromise between control ofadditive ringing effects and maximization of resolution anddepth-of-focus performance.

Furthermore, state of the art semiconductor dice often include closelyspaced or nested features as well as features which are isolated. Itwould, therefore, be an improvement in the art to provide an APSM thatincludes highly attenuated regions (i.e., attenuating regions allowingabout 4% to about 10% transmittance of incident radiation) wherenecessary to control additive ringing but also includes slightlyattenuated regions (i.e., attenuating regions allowing about 12% toabout 20% transmittance of incident radiation) where isolated devicefeatures are to be formed. Such an APSM would enable control of additiveringing effects where needed without compromising resolution anddepth-of-focus performance where additive ringing effects are of littleor no concern.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses the foregoing needs by providing an APSMthat, in each embodiment, includes completely transmissive regions sizedand shaped to define desired device features, slightly attenuatedregions at the edges of completely transmissive regions corresponding toisolated device features, highly attenuated regions at the edges ofcompletely transmissive regions corresponding to closely spaced ornested device features, and completely opaque areas where it isdesirable to block transmission of all radiation through the APSM. Thepresent invention further provides methods for fabricating the APSMsaccording to the present invention.

In one embodiment, the method of fabricating an APSM according to thepresent invention includes providing a transparent substrate. Thetransparent substrate is coated with a first attenuating layer thatshifts the phase of transmitted radiation by 180° and is only slightlyattenuated. The first attenuating layer is coated with a secondattenuating layer that does not shift the phase of passing radiation,but further attenuates the intensity of any radiation passingtherethrough. An opaque layer is then formed over the second attenuatinglayer. Using this intermediate structure, a desired APSM according tothe present invention may be formed.

To form a desired APSM, the opaque layer is coated with a resist. Theresist is then patterned to create a first patterned resist defining thesemiconductor die feature pattern to be projected by the finished APSM.The opaque layer is then etched.

After the opaque layer is etched, the first patterned resist may be leftin place and the second and first attenuating layers may be etched usingthe first patterned resist as a template. The first patterned resist isthen stripped, leaving a first intermediate mask structure includingcompletely transmissive regions corresponding to the pattern to beprojected by the mask and completely opaque regions where the opaquelayer and first and second attenuating layers remain intact.Alternatively, the first patterned resist may be removed after etchingthe opaque layer, and the opaque layer alone may be used as the templatefor etching the first and second attenuating layers.

A second layer of resist is deposited over the first intermediate maskstructure. The second layer of resist is patterned to define a secondpatterned resist, which exposes areas of the intermediate mask structurewherein slightly attenuated regions will be formed. The opaque layer andthe second attenuating layer in the areas exposed by the secondpatterned resist are then etched, revealing slightly attenuating regionsformed from portions of the first attenuating layer. The secondpatterned resist is then stripped, and the resulting second intermediatemask structure includes completely transmissive regions sized and shapedin accordance with the device pattern to be projected by the mask,slightly attenuated regions, which shift passing radiation one hundredeighty degrees (180°), and opaque regions where the opaque layer, aswell as the first and second attenuating layers, remain intact.Preferably, the slightly attenuated regions are provided at the edges ofeach of the completely transmissive regions corresponding to isolateddevice features, thereby maximizing image resolution and depth-of-focusperformance where it is not necessary to increase attenuation to combatthe negative effects produced by additive side lobes.

A third resist is deposited over the second intermediate mask structure.The third resist is then patterned to form a third patterned resist,which exposes areas of the second intermediate mask structure whereinhighly attenuated regions will be formed. The areas exposed by the thirdpatterned resist are then etched to remove only the opaque layer,thereby defining regions were incident radiation is phase shifted onehundred eighty degrees (180°) and highly attenuated as it passes throughboth the first and second attenuating layers. Preferably, such highlyattenuated regions are formed at the edges of completely transmissiveregions corresponding to closely spaced or nested device features,thereby increasing the resolution of such semiconductor die featuresprojected by the finished mask, while minimizing or eliminating anydefects from additive ringing effects.

The third patterned resist is then stripped leaving a completed maskaccording to the present invention. The completed mask, therefore,includes completely transmissive regions corresponding to the pattern tobe projected by the mask, slightly attenuated regions, which phase shiftpassing radiation one hundred eighty degrees (180°), highly attenuatedregions, which also shift passing radiation 180°, and opaque regionswhere the opaque layer and first and second attenuating layers remainintact.

As can be appreciated, the method of the present invention is highlyadaptable and can be used to fabricate APSMs having any desired featurepattern. Moreover, the steps of the method can be modified in severalaspects while still obtaining a desired APSM. For example, etch stoptechniques can be incorporated into the method of the present inventionto eliminate one or more etching steps. However, in each of itsembodiments, the method of the present invention advantageously producesAPSMs including completely transmissive regions, slightly attenuatedregions, and highly attenuated regions, and the size, shape, andposition of these various regions can be modified or adjusted to produceany desirable semiconductor die feature pattern.

Other features and advantages of the present invention will becomeapparent to those of skill in the art through a consideration of theensuing description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The figures presented in conjunction with this description are notactual views of any particular portion of a device or component, but aremerely representations employed to more clearly and fully depict thepresent invention.

FIG. 1 provides a schematic illustration of a prior art APSM as well asa graph depicting the electromagnetic intensity of radiation projectedthrough the prior art APSM;

FIG. 2 provides a schematic illustration of a second prior art APSM aswell as a graph depicting the electromagnetic intensity of radiationprojected through the second prior art APSM;

FIG. 3 schematically illustrates a cross-section of a partiallyfabricated semiconductor device structure after exposure through thesecond prior art APSM illustrated in FIG. 2;

FIG. 4 schematically illustrates a cross-section of a first intermediatemask structure formed in the first embodiment of the method of thepresent invention;

FIG. 5 schematically illustrates a first patterned resist formed overthe first intermediate mask structure of FIG. 4;

FIG. 6 provides a schematic illustration of a second intermediate maskstructure formed in the first embodiment of the method of the presentinvention;

FIG. 7 schematically illustrates the intermediate mask structuredepicted in FIG. 6, after a second patterned resist for creatingslightly attenuated regions is formed thereover;

FIG. 8 provides a schematic illustration of a third intermediate maskstructure formed in the first embodiment of the method of the presentinvention;

FIG. 9 and FIG. 10 schematically illustrate the third intermediate maskstructure depicted in FIG. 8, after a third patterned resist forcreating highly attenuated regions is formed thereover and the resultingstructure is subjected to a selective etch process;

FIG. 11 schematically illustrates a first embodiment of the APSM of thepresent invention;

FIG. 12 schematically illustrates a cross-section of a firstintermediate mask structure formed in the second embodiment of themethod of the present invention;

FIG. 13 schematically illustrates a first patterned resist formed overthe first intermediate mask structure of FIG. 12;

FIG. 14 provides a schematic illustration of a second intermediate maskstructure formed in the second embodiment of the method of the presentinvention;

FIG. 15 schematically illustrates the intermediate mask structuredepicted in FIG. 14, after a second patterned resist for creatingslightly attenuated regions is formed thereover;

FIG. 16 provides a schematic illustration of a third intermediate maskstructure formed in the second embodiment of the method of the presentinvention;

FIG. 17 and FIG. 18 schematically illustrate the third intermediate maskstructure depicted in FIG. 16, after a third patterned resist forcreating highly attenuated regions is formed thereover and the resultingstructure is subjected to a selective etch process; and

FIG. 19 schematically illustrates a second embodiment of the APSM of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the method of forming an APSM according to thepresent invention is schematically illustrated in drawing FIG. 4 throughdrawing FIG. 11. In each of these figures, the structures representingthe various intermediate APSM structures, as well as the complete APSM,are greatly simplified for ease of description.

As is illustrated in drawing FIG. 4, the method of the present inventionincludes providing a transparent substrate 60, such as quartz, fusedsilica, or other type glass substrates, etc. The transparent substrate60 is then coated with a first attenuating layer 62, such as a layer ofchromium oxynitride (CrO_(x)N_(y)) or chromium fluoride (CrF_(x)). Thefirst attenuating layer 62 is preferably highly transmissive (i.e.,allows about 12%-20% transmission) and shifts a phase of any passingradiation by 180°. The first attenuating layer 62 is then coated with asecond attenuating layer 64, such as a layer of molybdenum silicideoxynitride (MoSiO_(x)N_(y)). The second attenuating layer 64 is formedsuch that the second attenuating layer 64 does not shift the phase ofpassing radiation, but simply further attenuates the intensity of anypassing radiation. Preferably, the total attenuation of radiationpassing through the first attenuating layer 62 and the secondattenuating layer 64 is about 90% to about 96%, allowing about 4% toabout 10% transmission. An opaque layer 66, for example, a layer ofchromium, is then formed over the second attenuating layer 64, resultingin a first intermediate mask structure 70 that may be used to form adesired mask according to the first embodiment of the APSM of thepresent invention.

As is illustrated in drawing FIG. 5, to form a desired APSM according tothe first embodiment of the APSM of the present invention using thefirst intermediate mask structure 70, a first patterned resist 72 isformed over the opaque layer 66. The first patterned resist 72 is formedby first coating the opaque layer 66 with any suitable resist andpatterning the resist by known methods to define a desired featurepattern to be projected by the completed mask. After formation of thefirst patterned resist 72, the opaque layer 66 is etched to reveal areasof the second attenuating layer 64. Any suitable etch process may beused to etch the opaque layer. For example, where the opaque layerincludes chromium, a Cl₂/O₂ plasma etch process or a suitable wet etchprocess may be used to etch the opaque layer 66.

After the opaque layer 66 is etched, the first patterned resist 72 maybe left in place. The second attenuating layer 64 and the firstattenuating layer 62 may then be etched using the first patterned resist72 as a template, revealing the underlying transparent substrate 60 andforming various completely transmissive regions 74 a-74 f (shown indrawing FIG. 6), which correspond in size, shape, and location to thedevice pattern to be projected by the completed APSM. The secondattenuating layer 64 and first attenuating layer 62 are etched using anysuitable method. However, where the second attenuating layer 64 includesMoSiO_(x)N_(y), an SF₆ or CF₄ based plasma etch process is preferablyused, and where the first attenuating layer 62 includes CrF_(x), thefirst attenuating layer 62 is preferably etched in a Cl₂/O₂ plasma.Moreover, where it is used as a template for the formation of thecompletely transmissive regions 74 a-74 f, the first patterned resist 72is stripped after the completely transmissive regions 74 a-74 f areformed, leaving a second intermediate mask structure 76, which isillustrated in drawing FIG. 6, including completely transmissive regions74 a-74 f.

Once the second intermediate mask structure 76 is formed, slightlyattenuated regions are formed where desired. Slightly attenuated regionsare created using a second patterned resist 78 formed over the secondintermediate mask structure 76, as shown in drawing FIG. 7. The secondpatterned resist 78 is formed by first coating the first intermediatemask structure 76 with any suitable resist and patterning the resist byknown methods to create exposed areas 77 a and 77 b on the secondintermediate mask structure 76, wherein slightly attenuated regions areto be created.

As is shown in drawing FIG. 8, which illustrates a third intermediatemask structure 82, the slightly attenuated regions 80 a-80 d are createdby etching the opaque layer 66 and the second attenuating layer 64 inthe exposed areas 77 a and 77 b created by the second patterned resist78. Again, the opaque layer 66 and the second attenuating layer 64 caneach be etched by known etch processes, such as those already discussed.As can also be seen in drawing FIG. 8, the slightly attenuated regions80 a-80 d are preferably formed at the edges of isolated completelytransmissive regions 74 a, 74 f. Because the slightly attenuated regions80 a-80 d are formed using portions of the first attenuating layer 62,which shifts transmitted radiation 180°, radiation transmitted throughthe slightly attenuated regions 80 a-80 d destructively interferes withradiation diffracting out from the edges of the isolated completelytransmissive regions 74 a, 74 f, thereby greatly increasing theresolution with which the isolated completely transmissive regions 74 a,74 f define desired device features. Moreover, because slightlyattenuated regions 80 a-80 d allow transmission of about 12% to about20% of the incident radiation, the slightly attenuated regions 80 a-80 dserve to maximize depth-of-focus performance.

As shown in drawing FIG. 9, to create highly attenuated regions wheredesired, a third patterned resist 84 is formed over the thirdintermediate mask structure 82. The third patterned resist 84 is createdby first coating the third intermediate mask structure 82 with asuitable resist. The resist is then patterned by known methods to exposean area 85 of the third intermediate mask structure 82 wherein highlyattenuated regions are to be created.

Highly attenuated regions 86 a-86 e are then formed by selectivelyetching the opaque layer 66 in the exposed area 85 (see drawing FIG.10). The opaque layer 66 can be etched using any suitable etch process,such as the processes already discussed herein. After formation of thehighly attenuated regions, the third patterned resist 84 is stripped,leaving a complete APSM 88 according to the first embodiment of the APSMof the present invention (shown in drawing FIG. 11). It is easilyappreciated from reference to drawing FIG. 11 that the highly attenuatedregions 86 a-86 e are preferably formed at the edges of closely spacedtransmissive regions 74 b-74 e which are closely spaced. Because of theone hundred eighty degree (180°) phase shift provided by the firstattenuating layer 62 and the high total attenuation provided by thehighly attenuated regions 86 a-86 e, the highly attenuated regions 86a-86 e formed at the edges of closely spaced completely transmissiveregions 74 b-74 e greatly increase the resolution with which theisolated completely transmissive regions 74 a, 74 f define desireddevice features, while minimizing or eliminating any fabrication defectsthat may otherwise occur due to additive ringing effects.

As can be appreciated by reference to drawing FIG. 11, even afterformation of completely transmissive regions 74 a-74 f, slightlyattenuated regions 80 a-80 d, and highly attenuated regions 86 a-86 e,portions of the opaque layer 66 remain, forming opaque regions 90 a-90d. Opaque regions 90 a-90 d may be maintained on the finished APSM toprevent exposure to even attenuated radiation where attenuated radiationis not needed to increase image resolution. The first embodiment of themethod of the present invention, therefore, provides an APSM havingcompletely transmissive regions, highly attenuated regions, slightlyattenuated regions, and opaque regions, which work in concert tomaximize image resolution and depth-of-focus for isolated features,while minimizing or eliminating any defects caused by additive ringingeffects in areas of high feature density and preventing any defectscaused by transmission of attenuated radiation where attenuatedradiation is not needed to enhance resolution and depth-of-focus.

In a second embodiment, described in conjunction with drawing FIG. 12through drawing FIG. 19, the method of the present invention involvesthe use of etch stop technology. As illustrated in drawing FIG. 12, themethod of the second embodiment also involves providing a transparentsubstrate 60, which may also be, for example, a quartz, fused silica, orother glass substrate. A first attenuating layer 100 comprising CrF_(x)is deposited over the transparent substrate, followed by the formationof an etch stop layer 102 over the first attenuating layer 100. The etchstop layer 102 may be formed of any suitable etch stop material thatwill allow for an etch selectivity between it and the etching chemistryutilized to etch the material adjacent to it (i.e., second attenuatinglayer 104 shown in FIG. 12). For example, the first etch stop layer 102may be formed of silicon dioxide (SiO₂).

The first attenuating layer 100 is only slightly attenuating, allowingabout 12% to about 20% transmission. Moreover, the first attenuatinglayer 100 may be formed such that the first attenuating layer 100induces a one hundred eighty degree (180°) phase shift in radiationpassing through the first attenuating layer 100. Alternatively, thefirst etch stop layer 102 may be formed to induce a one hundred eightydegree (180°) phase shift, while the first attenuating layer 100 servesonly to attenuate passing radiation, or the first attenuating layer 100and first etch stop layer 102 may be formed such that radiation mustpass through both layers 100, 102 to be shifted one hundred eightydegrees (180°) out of phase. Where the first attenuating layer 100 isformed such that the first attenuating layer 100 both attenuates passingradiation and shifts the passing radiation one hundred eighty degrees(180°) out of phase, the first etch stop layer 102 is formed to allowpassage of radiation without inducing any further phase shifts.

As shown in drawing FIG. 12, a second attenuating layer 104 is formedover the etch stop layer 102. The second attenuating layer 104 is alsopreferably formed of CrF_(x) and further attenuates passing radiation.The second attenuating layer 104 is preferably formed such thatradiation passing through both the first attenuating layer 100 and thesecond attenuating layer 104 is highly attenuated (i.e., the combinedattenuation of the first attenuating layer 100 and the secondattenuating layer 104 is about 90% to about 96%, resulting in about 4%to about 10% transmittance). However, the second attenuating layer 104does not induce any phase shift in radiation passing therethrough. Oncethe second attenuating layer 104 is formed, an opaque layer 106 isprovided over the second attenuating layer 104, resulting in a firstintermediate mask structure 108. As is true in the first embodiment ofthe method of the present invention, the opaque layer 106 may be formedof any suitable material known in the art and by any suitable method,such as a deposited chromium layer.

Using the first intermediate mask structure 108, an APSM according tothe second embodiment of the APSM of the present invention may befabricated. Forming an APSM according to the second embodiment using thefirst intermediate mask structure 108 involves formation of a firstpatterned resist 110 over the opaque layer 106 of the first intermediatemask structure 108, as is shown in drawing FIG. 13. The first patternedresist 110 is created by first coating the opaque layer 106 with anysuitable resist and patterning the resist by known methods to define thedesired feature pattern to be projected by the completed APSM. Afterformation of the first patterned resist 110, the opaque layer 106 andthe second attenuating layer 104 are etched in a single step using aCl₂/O₂ plasma etch process, which will stop at the etch stop layer 102.With the first patterned resist 110 still in place, the etch stop layer102 is etched using a fluorine-based plasma etch process, and the firstattenuating layer 100 is then etched using a second Cl₂/O₂ plasma etchprocess.

After etching the first attenuating layer 100, the first patternedresist 110 is stripped, leaving a second intermediate mask structure112, as illustrated in drawing FIG. 14. The second intermediate maskstructure 112 includes completely transmissive regions 114 a-114 f whichcorrespond in size, shape and location to the device pattern to beprojected by the mask.

As can be seen in drawing FIG. 15, a second patterned resist 116 is thenformed over the second intermediate mask structure 112, in order to formslightly attenuated regions where desired. The second patterned resist116 is formed by first coating the second intermediate mask structure112 with any suitable resist and patterning the resist by known methodsto create exposed areas 118 a, 118 b of the second intermediate maskstructure 112 wherein slightly attenuated regions are to be formed.

As can be appreciated by reference to drawing FIG. 16, which illustratesa third intermediate mask structure 120, slightly attenuated regions 122a-122 d are then created by etching the opaque layer 106 and the secondattenuating layer 104 in a single step using a Cl₂/O₂ plasma etchprocess, which stops at exposed portions 124 a-124 d of the etch stoplayer 102, thereby reducing the number of etch steps necessary to formthe slightly attenuated regions 122 a-122 d relative to the firstembodiment of the method of the present invention.

Further illustrated in drawing FIG. 16 is that the slightly attenuatedregions 122 a-122 d, are preferably formed only at the edges of isolatedcompletely transmissive regions 114 a, 114 f. Because the slightlyattenuated regions 122 a-122 d are formed of portions of the firstattenuating layer 100 as well as portions of the etch stop layer 102,the slightly attenuating regions 122 a-122 d shift transmitted radiationone hundred eighty degrees (180°), and the radiation transmitted throughthe slightly attenuated regions 122 a-122 d destructively interfereswith radiation diffracting out from the edges of the isolated completelytransmissive regions 114 a, 114 f, thereby greatly increasing theresolution with which the isolated completely transmissive regions 114a, 114 f define desired device features. Moreover, because slightlyattenuated regions 122 a-122 d allow transmission of about 12% to about20% of the incident radiation, the slightly attenuated regions 122 a-122d serve to maximize depth-of-focus performance.

As illustrated in drawing FIG. 17, a third patterned resist 128 isformed over the third intermediate mask structure 120 to create highlyattenuated regions where desired. The third patterned resist 128 iscreated by first coating the third intermediate mask structure 120 withany suitable resist. The resist is then patterned by known methods toexpose an area 130 of the third intermediate mask structure 120 whereinhighly attenuated regions are to be created.

Highly attenuated regions 132 a-132 e are then formed by selectivelyetching the opaque layer 106 in the exposed area 130 (see drawing FIG.18). Though the opaque layer 106 can be etched using any suitable etchprocess, where chromium is used as the opaque layer 106, for example, aCl₂/O₂ plasma etch process or a suitable wet etch process may be used.After formation of the highly attenuated regions 132 a-132 e, the thirdpatterned resist 128 is stripped, leaving a complete APSM 134 accordingto the second embodiment of the APSM of the present invention (shown indrawing FIG. 19).

As was true in the first embodiment of the APSM of the presentinvention, the highly attenuated regions 132 a-132 e included in thesecond embodiment of the APSM 134 of the present invention arepreferably formed at the edges of the closely spaced completelytransmissive regions 114 b-114 e. The one hundred eighty degree (180°)phase shift provided by the first attenuating layer 100 and/or the etchstop layer 102 and the high total attenuation provided by the combinedattenuations of the first attenuating layer 100 and the secondattenuating layer 104, enhance the resolution of the images projected bythe closely spaced completely transmissive regions 114 b-114 e, whileminimizing or eliminating any fabrication defects that may otherwiseoccur due to additive side lobes produced by the closely spacedcompletely transmissive regions 114 b-114 e.

Reference to drawing FIG. 19 highlights that, even after formation ofcompletely transmissive regions 114 a-114 f, slightly attenuated regions122 a-122 d, and highly attenuated regions 132 a-132 e, portions of theopaque layer 106 remain, forming opaque regions 140 a-140 d. Again,opaque regions 140 a-140 d may be maintained on the finished APSM toprevent exposure to even attenuated radiation where attenuated radiationis not needed to increase image resolution. The second embodiment of themethod of the present invention, therefore, also provides APSMs havingcompletely transmissive regions, highly attenuated regions, slightlyattenuated regions, and opaque regions, which work in concert tomaximize image resolution and depth-of-focus for isolated features,while minimizing or eliminating any defects caused by additive ringingeffects in areas of high feature density and preventing any defectscaused by transmission of attenuated radiation where attenuatedradiation is not needed to enhance resolution and depth-of-focus.

Though the method and APSM of the present invention have been describedand illustrated herein with reference to two different embodiments, suchdescriptions and illustrations do not limit the scope of the presentinvention. The method of the present invention and design of an APSMaccording to the present invention are highly adaptable. For example,the method disclosed herein can be used to fabricate APSMs having anydesired feature pattern. Moreover, the steps of the method andcomposition of the APSMs can be modified in several aspects while stillobtaining an APSM according to the present invention. For instance, themethod of the present invention may utilize etching processes differentfrom those discussed herein. Additionally, materials different thanthose described herein, such as, different substrate materials,different attenuating materials, different light blocking materials, ordifferent etch stop materials, may be used in conjunction with themethod of the present invention to fabricate APSMs according to thepresent invention having a different material composition than the APSMsaccording to the first and second embodiments. Therefore, the presentinvention is not to be defined or limited by the illustrative anddescriptive examples provided herein, but, instead, the scope of thepresent invention is defined by the appended claims.

1. A fabrication method for an attenuated phase shift mask for a substrate having a first layer of attenuating material over said substrate, having a second layer of attenuating material over said first layer of attenuating material, and having an opaque layer over said second layer of attenuating material, the fabrication method comprising: etching said substrate to form at least one completely transmissive region; etching said substrate to form at least one slightly attenuated region, said etching including forming a second patterned resist over said substrate; and etching said substrate to form at least one highly attenuated region.
 2. The method according to claim 1, wherein etching said substrate to form said at least one completely transmissive region comprises forming a first patterned resist over said opaque layer of said substrate and etching said substrate to form a plurality of isolated completely transmissive regions and a plurality of closely-spaced completely transmissive regions.
 3. The method according to claim 2, wherein etching said substrate to form said at least one slightly attenuated region comprises removing portions of said opaque layer and said second layer of attenuating material to form a plurality of slightly attenuated regions, each of said plurality of slightly attenuated regions being positioned at an edge defining one of said plurality of isolated completely transmissive regions.
 4. The method according to claim 3, wherein etching said substrate to form said plurality of slightly attenuated regions comprises forming a second patterned resist over said substrate.
 5. The method according to claim 2, wherein etching said substrate to form said at least one highly attenuated region comprises removing portions of said opaque layer to form a plurality of highly attenuated regions, each of said plurality of highly attenuated regions being positioned at an edge defining one of said plurality of closely-spaced completely transmissive regions.
 6. The method according to claim 5, wherein etching said substrate to form said plurality of highly attenuated regions comprises forming a third patterned resist over said substrate.
 7. The method according to claim 1, wherein providing said substrate further comprises providing said substrate comprising an etch stop layer between said first layer of attenuating material and said second layer of attenuating material.
 8. The method according to claim 7, wherein etching said substrate to form said at least one completely transmissive region comprises forming a first patterned resist over said opaque layer of said substrate and etching said substrate to form a plurality of isolated completely transmissive regions and a plurality of closely-spaced completely transmissive regions.
 9. The method according to claim 8, wherein etching said substrate to form said at least one slightly attenuated region comprises removing portions of said opaque layer and said second layer of attenuating material in a single etch step to form a plurality of slightly attenuated regions, each of said plurality of slightly attenuated regions being positioned at an edge defining one of said plurality of isolated completely transmissive regions.
 11. The method according to claim 9, wherein etching said substrate to form said at least one highly attenuated region comprises removing portions of said opaque layer to form a plurality of highly attenuated regions, each of said plurality of highly attenuated regions being positioned at an edge defining one of said plurality of closely-spaced completely transmissive regions.
 12. The method according to claim 11, wherein etching said substrate to form said plurality of highly attenuated regions comprises forming a third patterned resist over said substrate.
 13. An attenuated phase shift mask comprising: a transparent substrate; a plurality of isolated completely transmissive regions; a plurality of slightly attenuated regions, each of said plurality of slightly attenuated regions being formed at an edge defining one of said plurality of isolated completely transmissive regions; a plurality of completely transmissive regions; and a plurality of highly attenuated regions, each of said plurality of highly attenuated regions being formed at an edge defining one of said plurality of isolated completely transmissive regions, said plurality of highly attenuated regions comprising a first layer of attenuating material, a layer of etch stop material, and a second layer of attenuating material.
 14. The attenuated phase shift mask of claim 13, further comprising a plurality of opaque regions, each opaque region of the plurality of opaque regions comprising chromium.
 15. The attenuated phase shift mask of claim 13, wherein said transparent substrate comprises a material selected from a group consisting of quartz, fused silica, and glass.
 16. The attenuated phase shift mask of claim 13, wherein said plurality of slightly attenuated regions comprises a layer of attenuating material selected from a group consisting of chromium oxynitride and chromium fluoride.
 17. The attenuated phase shift mask of claim 13, wherein said plurality of highly attenuated regions comprises a first layer of attenuating material and a second layer of attenuating material
 18. The attenuated phase shift mask of claim 17, wherein said first layer of attenuating material is selected from a group consisting of chromium oxynitride and chromium fluoride and said second layer of attenuating material comprises molybdenum silicide oxynitride.
 19. The attenuated phase shift mask of claim 13, wherein said plurality of slightly attenuated regions comprises a layer of attenuating material and a layer of etch stop material.
 20. The attenuated phase shift mask of claim 19, wherein said layer of attenuating material is selected from a group consisting of chromium oxynitride and chromium fluoride and said layer of etch stop material comprises silicon dioxide. 